Temper tantrum when asked to fix his mistake

On 23 Oct 2015 my car's head lights, brake lights and tail lights were repaired by Carel's Auto Electrician. All the lights worked when I fetched my car, and I paid him for the job. This morning I found out that the brake lights did not work. I took the car back, and Carel told me that he does not guarantee his work, I would have to pay again for any work done. He then let his assistant work on my car. The assistant took out a piece of loose wire, and when I asked him what the wire was for, he was rude and told me \I don't know"(sic). I then went to Carel to complain"